Correlation of the role of Li-doping in control of O-vacancies and Li-interstitial formations in NiO with electrochemical properties

Monovalent doping in a divalent cationic oxide material like NiO introduces modifications in the cationic valence state of the lattice and differences in the ionic radii of the cationic site. Such modifications introduce changes in the oxygen lattice and can introduce interstitial cationic sites, thereby increasing the strain and disorder in the lattice and modifying the bond lengths, leading to changes in the electronic, transport, and capacitive properties, which results in modifications in the charge storage properties. Monovalent Li⁺doping in NiO is commonly noticed in literature. However, an attempt to correlate the defect formation and associated changes in structural, vibrational, and electronic properties and thereby correlate these to the charge storage properties has not been made. In a first-of-its-kind report, this work reveals that the charge storage properties improve until 3% Li⁺substitution and thereafter decrease for 6%. The defect study of these materials hints at Li-interstitial being the responsible factor behind such degradation. The connection of oxygen defects, and Ni²⁺to Ni³⁺transformation seems to increase the charge storage.